One of the problems associated with rocket powered vehicles is the extent of the space envelope required to store the rocket motor with its usually large and awkward to store expansion cone. A way to shorten the cone and to decrease its diameter for storage has been devised, however, and is available in the form of a skirt attached to the exit rim of the motor's expansion cone but which can be folded into the motor's open end to decrease the expansion cone's dimensions considerably. Folding expansion cones of various sorts are known in the rocket motor art as is shown, for instance, in U.S. Pat. No. 4,125,224 to Lee F. Carey which shows an extendible and expansible pleat-folded skirt.
A particular problem exists in such devices, however, in that they operate so quickly upon ignition of the motor that interference of the skirt may occur with surrounding structure, for instance, in the event of stage separation in a multi-stage rocket system where the skirt may hit upon the separating stage before it is entirely clear of the first stage and possibly cause damage to the skirt or to other parts with resulting loss of performance or malfunction. The present invention solves this problem by including a liner or barrier of ablative or sacrificial material within the expansion cone of the rocket motor ahead of the folded deployable skirt which serves to block the flow of combustion gases to the skirt until the barrier has been eroded away. With the barrier thus removed, the skirt is acted upon by the gases and becomes deployed but only after the period of time required for barrier consumption has expired, thus giving time for the rocket stages to separate sufficiently to avoid interference.